This application claims priority from Korean Patent Application No. 2002-46175, filed on Aug. 5, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a field emission display, and more particularly, to a field emission display with separate upper electrodes.
2. Description of the Related Art
Field emission displays, like cathode ray tubes (CRTs), display a color image by emitting light of a predetermined color through the bombardment of electrons onto a field emitter array (FEA) coated with phosphor.
The simplest way to display color images on field emission displays is a pixel-to-pixel method or a cathode switching method. In the pixel-to-pixel method, each pixel includes phosphors of different colors arrayed on corresponding anodes. A cathode is driven to hit a phosphor of a desired color with electrons.
FIG. 1 is a sectional view of a conventional field emission display utilizing the switching method. In FIG. 1, “∘” denotes applying voltage, and “X ” denotes not applying voltage.
Referring to FIG. 1, a field emitter array (FER) 20, including a plurality of emitters 26R, 26G, 26B, 28R, 28G, and 28B, is formed on a cathode 11 and faces an anode 13. Sequences of red, green, and blue phosphors 16R, 16G, and 16B and 18R, 18G, and 18B are arranged on the anode 13 and aligned with the respective emitters 26R, 26G, 26B, 28R, 28G, and 28B. A first pixel 16 includes red, green, and blue phosphors 16R, 16G, and 16B, and a second pixel 18 includes red, green, and blue phosphors 18R, 18G, and 18B. For the convenience of illustration, only two pixels 16 and 18 appear in FIG. 1
The anode 13 is a common electrode through which a voltage is applied to all of the red, green, and blue phosphors 16R, 16G, 16B, 18R, 18G, and 18B, whereas the cathode 11 is comprised of individual electrodes arranged in rows and columns, through which a voltage is selectively applied to those emitters among the emitters 26R, 26G, 26B, 28R, 28G, and 28B that face phosphors of desired colors.
According to the cathode switching method, in order to emit violet (V) light 31 through the first pixel 16, a common voltage is applied to the anode 13, and a voltage is applied only to the emitters 26R and 26B facing red phosphor 16R and blue phosphor 16B to simultaneously emit red light and blue light. In order to emit green light G through the second pixel 18, a common voltage is applied to the anode 13, a voltage is applied to operate only the emitter 28G facing green phosphor 18G to emit green light. The cathode switching method of selectively driving an emitter facing phosphor of a desired color is simple.
However, the cathode switching method may cause cross talk between different colors of light.
For a higher resolution field emission display, phosphors 16R, 16G, 16B, 18R, 18G, and 18B are spaced to be closer together, and the size of the emitters 26R, 26G, 26B, 28R, 28G, and 28B is reduced. When such a higher resolution field emission display is driven using the above-described cathode switching method and an equal amount of voltage is simultaneously applied to all of the red, green, and blue phosphors 16R, 16G, 16B, 18R, 18G, and 18B, electrons emitted from the emitter 26R, which is for exciting red phosphor 16R, may hit green phosphor 16G. Such cross talk degrades color purity or quality of displayed images.
Such a cross-talk phenomenon is illustrated in FIG. 2. Electrons emitted from the emitter 26B, which is for exciting blue phosphor 16B, may reach adjacent green phosphor 16B or red phosphor 18R and emit undesired green or red light. Electrons emitted from the emitter 28G, which is for exciting green phosphor 18G, may reach adjacent red phosphor 18R or blue phosphor 18B.
In addition to the problem of cross talk, the cathode switching method requires more, smaller emitters corresponding to each color of phosphor, so that it is difficult to manufacture and assemble such emitters in a device.
An anode switching method can be applied to drive a color field emission display. In the anode switching method, emitters are designed to excite phosphors of different colors in each frame, and each emitter corresponds phosphors of to the three primary colors.
FIG. 3 is a sectional view of a conventional field emission display utilizing an anode switching method.
Referring to FIG. 3, emitters 20a and 20b are arranged on a cathode 11 facing an upper substrate 12. A red phosphor 16R, a green phosphor 16G, a blue phosphor 16B, a red phosphor 18R, a green phosphor 18G, and a blue phosphor 18B are arranged on the upper substrate 12 such that each group of red, green, and blue phosphors is aligned with a respective one of the emitters 20a and 20b. A first pixel 16 includes the red, green, and blue phosphors 16R, 16G, and 16B, which correspond to the emitter 20a, and a second pixel 18 includes the red, green, and blue phosphors 18R, 18G, and 18B, which correspond to the emitter 20b. First through third anodes 13a, 13b, and 13c are formed in the upper substrate 12. The first anode 13a is connected to the red phosphor 16R in the first pixel 16 and the red phosphor 18R in the second pixel 18. The second anode 13b is connected to the green phosphor 16G in the first pixel 16 and the green phosphor 18G in the second pixel 18. The third anode 13c is connected to the blue phosphor 16B in the first pixel 16 and the blue phosphor 18B in the second pixel 18.
In order to emit violet (V) light 31 through the first pixel 16, as illustrated in (a) of FIG. 3, a voltage is applied to the first anode 13a connected to the red phosphor 16R, and a voltage is applied to the cathode 11 to drive only the emitter 20a corresponding to the red phosphor 16R. In other words, only the emitter 20a of the first pixel 16 is driven to emit electrons, and a voltage is applied to the first anode 13a to allow only the red phosphor 16R connected to the first anode 13a to be excited by the bombardment of the electrons, so that red light is emitted through the first pixel 16.
Next, as illustrated in (b) of FIG. 3, a voltage is applied to the third anode 13c connected to the blue phosphor 16B, and a voltage is applied to the cathode 11 to drive only the emitter 20a corresponding to the blue phosphor 16B, so as to bombard and excite only the blue phosphor 16B with electrons emitted from the emitter 20. As a result, blue light is emitted from the first pixel 16 a short time lag after the emission of the red light so that violet (V) light 31 is perceived from the first pixel 16.
In order to emit green (G) light 33 through the second pixel 18, as illustrated in (c) of FIG. 3, a voltage is applied only to the second anode 13b connected to the green phosphor 18G in the second pixel 18, and a voltage is applied to the cathode 11 to allow only the emitter 20b corresponding to the green phosphor 18G to emit electrons, so that green light is emitted from green phosphor 18G in the second pixel 13.
Unlike the cathode switching method, the anode switching method involves selectively applying a voltage to an anode aligned with a phosphor of a desired color. Accordingly, emitted electrons can be more accelerated toward the phosphor. In addition, the overall manufacturing process is simplified because each emitter needs not to be arranged to be aligned with each color of phosphor. However, the anode switching method requires individual anodes to be separately insulated in order to make it possible to selectively apply a voltage to an anode to obtain a desired color. Insulating three anodes, aligned with each emitter, on a 2-dimensional plane is complicated. In addition, it is impossible to apply a high voltage to the anodes due to the inherent characteristics of insulating materials. The voltage applied to the anodes is lower than when using the cathode switching method, so that the luminance of images displayed on pixels is greatly degraded.